Good plan for a CAAD3?

I'm new to the forum and dumb as this post...

I do know that I love cycling the network of old timber and oil well roads around my home in south Arkansas. I now use a Cannondale ST400 (ST=sports touring). I like the stiff frame and gear range, but some of these roads are too rough for 27" wheels, and I stay busy fiddling with downtube shifters when I hit small hills. In short, I'm not so much an off-roader as someone who bikes 10-25 miles of rough asphalt and gravel/dirt roads several times a week, and I need to find a better bike for the job.

I've found a Cannondale CAAD3 mountain bike frame in my size with a solid P-bone fork (probably a 1996 M500, judging by color and specs the seller gave). Assuming it fits well, would this bike be both fun (quick-handling, agile) and comfortable enough for my morning ride? Do you think a carbon fork and seat post would make much difference in the weight or comfort level of the bike?